ARM: multi_v7_defconfig: Enable audio support for stm32mp157

This commits enable (as module):
- STM32 SAI and I2S configs used on stm32mp157.
- Cirrus CS42L51 audio codec for stm32mp157a-dk1 board.
- Audio graph card support for stm32mp157a-dk1 board.

Link: https://lore.kernel.org/r/20191025125632.11057-1-alexandre.torgue@st.com


Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Olof Johansson <olof@lixom.net>